Turbochargers enhance power output of an engine by directing exhaust flow from the engine to drive a turbine, which in turn drives a compressor. The compressor delivers the pressurized air into the intake manifold of the engine, and thus allows more fuel to be combusted. Since the turbine spins at high speeds, reaching 120,000 rpm or more, and is fluidically in communication with the exhaust system, the turbocharger and its housing can experience extremely high temperatures that may eventually deform various components. Because of these detrimental conditions, the housing of turbochargers may be manufactured from cast iron, which is very durable, but burdens the vehicle with significant weight that ultimately reduces fuel economy. Thus, in recent years, some manufacturers have instead opted to produce turbine housings from sheet metal.
Turbochargers comprising two layers of sheet metal provide a number of advantages over cast iron turbochargers. Because sheet metal may be manufactured into thinner pieces, the turbocharger may be lighter and thereby reduces the overall weight of the vehicle. Further still, sheet metal comparatively heats up more rapidly by the inlet exhaust gases, enabling components of the exhaust aftertreatment system, namely the catalytic converter, to reach operational (light off) temperatures more quickly on turbocharged engines, for both gasoline and diesel engines. This time to light off is prolonged when using cast iron for the turbocharger housing because of its higher heat absorption capacity.
On the other hand, the high temperature of exhaust gases, reaching temperatures upwards of 1050° C., may be more destructive to the sheet metal compared to the conventional cast iron, wherein the gathering inlet gases can distort the integrity of the sheet metal. More specifically, a turbine housing may undergo thermal expansion and thermal contraction occurring during a thermal cycle that accompanies an engine operation. When thermal deformation occurs in the turbine housing, a turbine tip clearance with the sheet metal turbine housing is typically more than doubled. In some cases, the tip clearance may increase from 0.4 to 1 mm for a turbine for light to medium duty diesel applications, which may translate into 8-12% efficiency loss or 1-3% fuel economy loss.
One example approach to address heat-induced deformation of a turbine housing is shown by Bogner et al. in U.S. patent application Ser. No. 13/984,894. Therein, a turbocharger having a coolant inlet, a cooling jacket provided in the interior of the turbine housing, and a coolant outlet is described. In this embodiment, a coolant jacket is disposed between two layers of a turbine housing.
However, the inventors herein have recognized potential issues with such systems. As one example, such cooling jackets are technically complex, require precision recasting of the turbine housing, and are correspondingly expensive to manufacture. In addition, integration with a turbocharger in a vehicle may require the turbine casing to be larger to accommodate the turbocharger, and thus lead to an increased front zone weight burden. Cooling jackets may also require complicated hydraulic and mechanical connections between the turbocharger and the internal combustion engine for the circulation of cooling fluid within the central body of the turbocharger. Even if these features may be incorporated, there may be no possibility of arranging a sufficiently large heat exchanger for liquid cooling of the turbine in the front end zone to allow dissipation of the large amounts of heat.
Accordingly, a turbine comprising a turbine housing surrounding a rotor is provided, wherein the turbine housing includes an inner layer and an outer layer of sheet metal, the outer layer surrounding the inner layer at a distance to form an intermediate space between the inner and outer layers. This intermediate space provides additional insulation and reduces heat losses. In addition, a reinforcement element comprising a body of corrugated or bellowed sheet metal having a cellular structure or a pattern is disposed in the intermediate space and coupled to at least one of, or both of, the inner and outer layers. The reinforcement element may be spaced at symmetrical or asymmetrical intervals for a limited distance or may be disposed along the entirety of the housing. In another example, the reinforcement may only be disposed at a specific location, such as between the inner and outer layers of the housing proximal to turbine blades. In this way, it is possible to maintain a threshold length between the inner layer and the rotor by strengthening the sheet metal layers closest to the turbine blades.
In one example, the reinforcement element makes it possible to dispense with materials with the capacity to bear high thermal stresses, but is burdensome in weight, such as cast iron, for the production of the turbine housing. The cellular configuration of the body of sheet metal of the reinforcement element may comprise a suitable repeating pattern. In one example, the pattern may embody a honeycomb-shaped structure, so that each face of a hexagon is in face sharing contact with the inner and/or outer layer of turbine housing. In other examples, the pattern may comprise various trigonometric geometries, such as a repeating sine wave. Further still, in other examples, the pattern may take on a generally square or triangular shape aligned in series. The reinforcement elements may be attached to the layers of the housing via spot-welding. Such patterns and attachment method provide desirable thermal-protective and structurally strengthening characteristics to the sheet metal housing layers.
Therefore, the technical effects achieved via the reinforcement element is an increase in thermal resistance and reduction of deformation in the turbine housing, and thus may help reduce an increase in distance between the turbine rotor and inner layer of the housing. As a result, loss to efficiency and fuel economy can be reduced.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.